Human plasma prokallikrein purified from plasmas of 3 individuals (one female, two males) of different race (Caucasoid, Mongoloid, and Negroid) in the presence or absence of DFP gave electrofocusing patterns indistinguishable from that found previously for pooled plasma fractionated in the absence of DFP. Human Hageman factor (factor XII) fragment(s) was obtained in highly purified form as assessed by its specific activities for TAME and plasma prokallikrein and by polyacrylamide gel electrophoresis. Of 66 plants tested for inhibitors of Hageman factor and plasma kallikrein, only corn contained a strong inhibitor for the former but no inhibitor for the latter enzyme. Human renal prokallikrein has been highly purified by immunoaffinity chromatography and gel filtration to the point that the zymogen can now be activated by catalytic amounts of trypsin. Renal kallikrein formed from purified prokallikrein either spontaneously or by trypsin activation has a slightly lower molecular weight than the zymogen.